1. Field of the Invention
The present invention concerns a quantitative organic vapor-particle sampler which can efficiently sample both semi-volatile organic gases and particulate components through the use of a unique sorbent resin coating and process.
The sampler of the present invention comprises in its broadest aspect a tubular device having an inlet at one end through which organic vapor/particles are introduced, an outlet at the other end through which gases exit, at least one annular denuder interposed therebetween which is coated on the inside surface of the annulus with a specially prepared resin absorbent, which selectively absorbs organic vapors contained in the gases introduced into the inlet, and a filter which traps and collects particles.
The invention further concerns a semi-volatile organic reversible gas sorbent for use in an integrated diffusion vapor-particle sampler comprising macroreticular resin agglomerates of randomly packed microspheres with the continuous porous structure of particles ranging in size between 0.05-10 .mu.m.
2. Background and Related Disclosures
Assessment of both the vapor and particle components of various samples is important in a number of different situations. Accurate measurements of phase distributions of polycyclic aromatic hydrocarbons (PAH) in indoor air and environmental tobacco smoke (ETS) are needed in order to assess exposure or danger of exposure to carcinogenic compounds since lung deposition patterns of PAH depend on the distribution of the PAH between the gas and particle phases. Environmental fates of semi-volatile organic species are also phase-dependent because atmospheric reactions, and transport and deposition processes differ for gas and particulate semi-volatile species. Understanding the contribution of organic species to visibility degradation requires accurate phase distribution data. Pollutant control strategies are also phase-dependent.
Classic vapor-particle samplers, generally termed filter-sorbents, allow flow of an air sample through a chamber. In these samplers, at the end of the chamber where the airstream enters the chamber is a physical filter that picks up the particulate matter from the sample, as well as any semi-volatile components associated with it. At the base of the chamber is a sorbent bed which then collects any remaining gas phase materials. These gas-phase materials are then desorbed and analyzed to determine the presence of the material in the sample.
Some specialized filter-sorbent samplers which can detect gas-phase organic polycyclic aromatic hydrocarbons (PAH) have been developed. Cotham et al., developed such a sampler using polyurethane foam for the sorbent (Environmental Science and Technology, Vol 26, pp 469-478, (1992)). Kaupp et al used macroreticular polymeric resin beads to test for PAH, which are described in (Atmospheric Environment, Vol 26A, pp 2259-2267, (1992).
Unfortunately, because these prior art sampler sorbent beds are positioned downstream from the filter, desorption of semi-volatile compounds from the filter creating negative artifacts, or collection of gases by the filter creating positive artifacts, lead to incorrect measurements of gas-phase and particle-phase concentrations. Considerable experimental and theoretical efforts have been expended to understand and correct for these condensation and vaporization effects.
An important advance in vapor-particle samplers was described by Possanzini in Atmospheric Environment, 16:845.gtoreq.853, (1983). The sampler described therein was able to test for inorganic acidic or basic gases using sorbents, such as sodium bicarbonate and citric acid. Additionally, Possanzini developed a different configuration for the sampler, allowing for greater efficiency while avoiding many of the problems of the prior art samplers.
In contrast to the prior art samplers, in Possanzini's configuration the sample is pulled through an annular space coated with a specific sorbent. The filter to collect the particulate portion of the sample is positioned downstream of the sorbent. This configuration obviates the positive and negative artifact problem of the prior art samplers.
The Possanzini configuration allows this arrangement because of the design and function of his sampler. Possanzini's sampler includes an annulus through which the sample flows by positioning two tubes concentrically to form such annulus. Other researchers have developed alternate means to produce the sample flow necessary for this sampling technique.
Broadly, Possanzini's improvement works as follows. When an airstream containing gases and particles is moving through tubes under conditions of laminar flow at a certain linear velocity, the particles move at the linear flow velocity. By contrast, the gases diffuse randomly in all directions at speeds determined only by their molecular weights and the temperature (kinetic energy).
When the airstream flows through an annulus, the dimension of the annulus (or annuli) is designed to be close to the diffusion path length of the gases. This results in the gases reaching the coated walls of the denuder where they react in an acid-base reaction. The gases are thus removed from the airstream, while the particle portion of the sample proceeds at the linear flow velocity of the airstream, to be removed by filtration. Any species desorbed from the filter are collected downstream of the filter.
The research community was very interested in sampling organic gases with the clearly superior efficiency using the Possanzini sampler. However, without a specific sorbent for organic components, this was not possible. Prior to the present invention, gaseous organic components could not be desorbed to make them available for analysis, much less to allow quantitative analysis.
Krieger et al (Environ. Sci. Technol., Vol 26 pp 1551-1555, 1992) developed a diffusion denuder to fill the need for quantitative analysis of semi-volatile gases, but due to its small size, this denuder had no capacity to test the particulate phase of a sample.
Krieger's diffusion denuder uses capillary gas chromatographic stationary phase columns that can be used for direct determination of gas-phase semi-volatile organics. This denuder is very effective at quantifying volatile organic compounds but less effective at quantifying semi-volatile organic compounds. This denuder has a lower capacity for gas-phase organic compounds than the integrated organic vapor-particle sampler of the instant invention.
In order to gain some of the advantages of the Possanzini approach for gaseous organic component analysis, some other differential diffusion samplers were developed where a sorbent was used only to clean the sample stream of volatile organic compounds, rather than serve in any testing capacity. In these systems, two separate sample chambers had to be constructed in order to test two aliquots of each sample, one with and one without the non-reversible sorbent present. Typically each side also had a sorbent downstream of the filter. It was then hoped that the difference in the collection on the filters and downstream denuders from each system would reflect the gaseous semi-volatile organic component of the sample. There was no quantitative finding available for any particular species in this "cleanse and test" system.
More recently, some other denuders were developed, such as, for example denuder, to cleanse the sample stream of semi-volatile organic species described in Environ. Sci. Technol., Vol 22 pp 941-947, (1988). Coutant et al, developed silicon grease (Atm. Environment, Vol. 26A pp 2831-2834, 1992) and Eatough et al, used filter paper impregnated with activated carbon as a denuder coating to collect semi-volatile organic compounds and pesticides (Atm. Environment, Vol. 27A pp 1213-1219, (1993)). Differential samplers represent an important advance over conventional samplers in the assessment of organic, gaseous species. However, as seen in U.S. Pat. No. 5,302,191, issued Apr. 12, 1994, sampling of atmospheric semi-volatile compounds remains a challenge, and is often inappropriately addressed by atmospheric chemists.
Recently, materials such as various resins have been utilized for coating surfaces of vapor-particle samplers, described above.
Meitzner in U.S. Pat. No. 4,224,415, incorporated hereby by reference, discloses a method of making a macroreticular resin by copolymerizing a mixture consisting of a monovinyl carbocyclic aromatic compound or an ester of acrylic or methyacrylic acid, with a polyethylenically unsaturated monomer selected from the group consisting of a polyvinyl carbocyclic aromatic compound, an ester of a dihydric alcohol and an .alpha.-.beta.-ethylenically unsaturated carboxylic acid, diallyl malcate, and divinyl ketone. The copolymerization was conducted while the monomers were dissolved in 25 to 150% by weight, based on monomer weight, of an organic liquid or mixture of organic liquids which acts as a solvent for said monomers but are unable to substantially swell the copolymers resulting from copolymerization.
However, these resins were not successfully utilized for efficient sampling of semi-volatile organic gases and particulate components and there still remain daunting limitations to the current integrated sampler technology in assessing volatile and semi-volatile gas species in a sample. While differential samplers address some of these needs, they require double equipment, and they require, as a prerequisite to obtaining correct results, that the sample be divided perfectly. Because the species in question is never directly recovered, it is impossible to achieve accurate quantitative results for any particular gaseous organic component.
A sorbent which can be adhered to the inner surface of an integrated sampler, and from which volatile and semi-volatile organic components can be desorbed and assessed quantitatively, would represent an important and dramatic advancement in atmospheric sampling.